1. Field of the Invention
This invention relates to a semiconductor device, specifically to the one in which a compound semiconductor layer is arranged on a substrate with a buffer layer interposed therebetween.
2. Description of the Related Art
Semiconductor light emitting devices and switching devices using Gallium Nitride (GaN) based compound semiconductor are generally known. Well-known semiconductor light emitting devices are a light emitting diode (LED), a semiconductor laser, and the like. Moreover, well-known switching devices are a high electron mobility transistor (HEMT), Schottky barrier diode (SBD), and the like.
Patent document 1 (U.S. Pat. No. 7,652,282 B2) discloses a semiconductor device including a main semiconductor region for HEMT formed of nitride compound semiconductor provided on a silicon substrate with a buffer formed of a nitride compound semiconductor interposed therebetween. The buffer layer includes a first multilayered buffer subregion formed on the silicon substrate and a second multilayered buffer subregion formed on the first multilayered buffer subregion. The first multilayered buffer subregion is formed by alternately laminating a multilayered buffer region (superlattice buffer region or sub multi-sublayered buffer region) of alternately laminating Al(Ga)N layers and (Al)GaN layers, and a non-sublayered buffer region of (Al)GaN layer. Similarly, the second multilayered buffer subregion is formed by alternately laminating a multilayered buffer region (superlattice buffer region or sub multi-sublayered buffer region) of alternately laminating Al(Ga)N layers and (Al)GaN layers, and a non-sublayered buffer region of (Al)GaN layer.
Thus configured semiconductor device in the patent document 1 can promote cancelling out stress generated in the first multilayered buffer subregion and stress generated in the second multilayered buffer subregion, thereby suppressing a warp of the silicon wafer. Furthermore, by suppressing the warp of the silicon wafer, the buffer layer and the main semiconductor region can be provided with greater thickness, thereby improving withstand voltage of the device in thickness direction.